There have been various known techniques of restraining occupants of motorcycles with airbag apparatuses. For example, a technique of restraining an occupant with an airbag inflated by inflation gas in a frontal collision (e.g., refer to Japanese Unexamined Patent Application Publication No. 2003-327182). The airbag apparatus disclosed in Japanese Unexamined Patent Application Publication No. 2003-327182 has a structure in which a prefolded airbag is housed in a housing; an airbag opening of the housing is covered with a cover (airbag cover); and the cover has a fragile portion that is easily torn open on the top. The cover is torn open along the fragile portion with the deploying motion of the airbag to open the airbag opening, thereby enabling the deploying motion of the airbag from the interior of the housing to the exterior.
However, when a load such as an occupant or a burden is applied onto the cover having a fragile portion at the top, as in the airbag apparatus described in Japanese Unexamined Patent Application Publication No. 2003-327182, the load is directly applied to the fragile portion, so that the cover may be torn open at the fragile portion. On the other hand, when the fragile portion itself is strengthened, the stress applied to the airbag and the housing is increased, so that the airbag and the housing must be strengthened, resulting in an increase in cost.